The short message service (“SMS”) provided by many cellular telephone companies is a service that permits the cellular customers to compose short text messages that can be transmitted via the network from the sender's cell phone to another cell phone and viewed on the other cell phone. In more recent years, these messages (commonly called SMSs themselves) can also contain other types of media, including audio clips and video clips. SMSs differ from conventional telephone calls because they are not a real time, two-way communication between the owners of the two cell phones. An SMS is more akin to an email in the sense that it is a one way communication from the sender to the receiver.
Due to this difference, communication networks tend to handle SMSs differently than voice calls in some respects. For instance, when one of the nodes involved in a conventional voice call between two cell phones is too overloaded to service all of the voice calls being made through that node at a given time, the overloaded node discards some of the voice calls. It is then up to each individual calling party whose call failed to try to make its call again.
On the other hand, since SMSs are not real-time two-way communications, when an SMS is discarded at a node, the node that sent the SMS typically continues to try to send the SMS repeatedly until it is successfully received by the target cellular telephone (or other device). Every network operates according to its specific design parameters. However, as an example, in the ANSI-41 protocol, the SMS sending node (i.e., a Short Message Service Center or SMSC) sends a Short Message Service Point to Point invoke message (hereinafter SMSDPP) containing the SMS to the SMS receiving node (i.e., a Mobile Switching Center or MSC) and typically waits to receive an acknowledgement message (i.e., a Short Message Service Point to Point return result or smsdpp return result) from the receiving node. If it does not receive the acknowledgment within a relatively short period of time, e.g., less than a minute (or if it receives a delivery failure notification; which is the protocol in certain networks), the sending node will assume the SMS did not reach its destination and send the SMS again. Typically, the sending node may try to send the SMS ten or more times in relatively quick succession before giving up.
Thus, this practice of resending an unacknowledged SMS to an overloaded node actually can exacerbate the overload condition at that node because every discarded message may cause the sending node to repeatedly send the same message over and over again in a reasonably short window, thus adding even more traffic to the overloaded node.
Furthermore, SMS messages do not contain any data as to priority of one SMS message relative to another or even whether the SMS is itself an acknowledgement message. Accordingly, an overloaded node that is discarding some portion of the SMSs it is receiving is discarding some of the SMSs and delivering others of the SMSs without any knowledge as to the importance of any of the SMSs.